Loss of control (LOC) eating is a health risk behavior that often originates and progresses during adolescence. Given its prospective associations with excess weight gain, worsening metabolic parameters, development of partial- or full-syndrome binge eating disorder, and increases in depressive symptoms, LOC eating may have negative physical and mental health consequences across the life span. Although negative emotions are considered a predictor of LOC eating in adults, children may have difficulty identifying and reporting their emotions and there is mixed support for the hypothesis that negative emotions predict LOC eating in children. For these reasons, physiologic indices of distress may be a feasible alternative predictor of LOC eating in youth. Heart rate (HR) and heart rate variability (HRV) reflect autonomic nervous system activity and they are considered markers of distress. In particular, high HR and low HRV reflect a combination of distress and reduced capacity to self-regulate in response to distress. We previously conducted an ecological momentary assessment (EMA) study in 17 adolescents in which HR and HRV were examined prior to eating episodes, and we found that higher HR and lower HRV were each associated with higher level of LOC eating. The broad aim of the current study is to conduct a follow-up EMA study of physiologic stress indices and LOC eating in a larger sample (n = 40) with a longer duration (7 days) per participant. Our specific aims are to investigate associations between physiologic indices (HR, HRV) and LOC eating (Aim 1), to investigate associations between physiologic indices (HR, HRV) and self-reported stress and negative mood (Aim 2), and to examine the trajectories of HR and HRV leading up to high- and low-LOC episodes (Exploratory Aim). Forty overweight/ obese adolescents with LOC eating will be recruited to complete a baseline screening visit, a 1-week EMA period, and a final visit. During the 1-week EMA period, adolescents will wear a chest strap with a biosensor during waking hours and they will use a smartphone to self-report stress, mood, and LOC eating at periodic intervals throughout the day. Adolescents will enter information on the smartphone in response to researcher- initiated ?beeps? and before and after eating. In order to evaluate relationships between physiologic indices and self-report constructs, segments of the continuous electrocardiogram recording that correspond with time- stamped self-report data from the smartphone will be extracted. Consistent with prior studies, 30-minute segments will be evaluated in relation to level of LOC, and 5-minute segments will be evaluated in relation to stress and negative mood. Consistent with conceptualization of LOC eating as a coping behavior, we hypothesize that there will be a positive relationship between HR and level of LOC, and an inverse relationship between HRV and LOC. We also expect that there will be a positive association between HR and stress and negative mood, and an inverse association between HRV and stress and negative mood. Studying physiologic predictors of LOC eating will inform its etiology and facilitate development of novel interventions.